Population Ecology

Population ecology - the study of all the individuals of a species within a given area at a given time.

Density and Dispersion (of populations)

Population density - Fig. 50.1
Measuring density

counting
sampling techniques
quadrats (sample plots)

transects

mark-recapture

Patterns of dispersion - Fig. 52.2

clumped dispersion - Fig. 52.2a - Fig. 52.2ax

uniform dispersion - Fig. 52.2b- Fig. 52.2bx
random dispersion - Fig. 52.2c- Fig. 52.2cx

Demography - Statistical Study of Populations

Age Structure - Fig. 52.22
Birth Rate or Fecundity - Table 52.2
Death Rate
Generation Time
Sex Ratio

Life Tables - cohort (See - Table 52.1 for example)
Survivorship Curves - Fig. 52.3

-- Type I
-- Type II
-- Type III

Life history - the traits that an individual expresses during its life. (Types of metamorphosis)

Timing of reproduction

semelparity - reproduce once and die - usually short-lived but salmon and agave - (Fig. 52.4) are exceptions
iteroparity - reproduce many times - usually long-lived

Trade-offs

current fecundity vs. adult survival (Fig 52.5 and Fig. 52.6)

number and size of offspring - larger and fewer - Fig. 52.7b or smaller and many - Fig. 52.7a
number of offspring & amount of parental care - fewer offspring, the greater amount; more offspring, less or no care

Population Growth

Exponential growth curve - Fig. 52.8 and Fig. 52.9

Reduction of r with increase in N - Fig. 52.10

Logistic growth curve - Fig. 52.11 - Table 52.3

N = number of individuals in population
t = elapsed time
b = average birth rate/individual in the population
d = average death rate/individual in the population
r = b- d = the intrinsic rate of increase
rmax is when the population is experiencing minimum death rate and maximum birth rate

K = carrying capacity

Examples of logistic population growth. - Fig. 52.12

Reproductive Strategies

r-selected (opportunistic) populations - characterized by exponential growth and sudden crashes
-- High intrinsic rate of growth (r)
-- Reproduce early, have many offspring
-- Offspring are small, mature rapidly, receive little parental care
-- Generations are relatively short, large brood size
-- Examples: dandelions, aphids, mice, cockroaches

K-selected (equilibrial) populations - Populations with sigmoid growth curves limited by carrying capacity (K)
-- Include relatively slow-breeding organisms
-- Tend to live in stable, predictable habitats
-- Reproduce late, have small broods
-- Offspring are large, mature slowly
-- Receive intensive parental care
-- Generations are relatively long
-- Examples: oaks, humans, whales

Many organisms are intermediate

Density-dependent factors - Fig. 52.13

Intraspecific competition and negative feedback

Decreased fecundity at high population densities - Fig. 52.14

Decreased survivorship at high population densities - Fig. 52.15

Density-independent factors